(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of silicidation wherein silicon stress is reduced in the fabrication of integrated circuits.
(2) Description of the Prior Art
Many benefits derive from silicided polysilicon gates and source/drain junctions. Nevertheless, recent investigations indicate that abnormal compressive stresses can be generated within the silicon substrate at the source/drain regions, especially near the shallow trench isolation (STI) corner or beneath the spacers during silicidation. These deleterious compressive stresses readily create defects at or in the vicinity of the interface between silicide and silicon. These defects have been diagnosed as the main culprit for high leakage current in the case of titanium silicidation. In addition, the compressive stresses induce the generation of high tensile stress within proximity regions, e.g. beneath the gate. The level of the tensile stress increases with the shrinking of gate length. Hence, the concomitant compressive stresses from source/drain silicidation have to be remedied effectively as well as efficiently.
FIG. 1 illustrates a portion of a partially completed integrated circuit. The semiconductor substrate 10 is preferably composed of silicon having a (100) crystallographic orientation. Gate electrode 16 and source/drain region 20 are formed in and on the semiconductor substrate as is conventional in the art. The source/drain junction has been silicided 22. The circles 23 indicate defects; leakage paths beneath the spacers and around the shallow trench isolation (STI). These are localized stress junctions. Stress junctions occur in regions where compressive stress from silicidation at the source/drain junction meets tensile stress at the spacer and the STI.
U.S. Pat. No. 5,683 924 to Chan et al teaches formation of a silicide film over epitaxial silicon or polysilicon raised source/drain regions. U.S. Pat. No. 6,001,697 to Chang et al discloses poly plugs over the source/drain junctions where silicidation is performed over the poly plugs. U.S. Pat. No. 5,879,997 to Lee et al discloses a polysilicon layer over the source/drain regions. The polysilicon is oxidized. Silicidation is not disclosed. U.S. Pat. No. 6,004,879 to Hu et al teaches a CoSixO contact material. None of the patents discuss stress relief during silicidation.